When a person has difficulty expelling all the air from her lungs, she's said to have an obstructive lung disease. An obstructive pattern exists when air moves out of the lungs at a slower rate than that of a healthy person. This occurs because inflammation and swelling (secondary to long-term, cumulative exposure to airway irritants) cause the airways to become narrow and blocked, making it difficult to completely rid the lungs of air. This leaves an abnormally high volume of air in the lungs after a full exhalation, which is referred to as "increased residual volume." In obstructive lung defects, increased residual volume leads to air getting trapped in, and hyperinflation of, the lungs two changes in the lungs that may contribute to worsening symptoms.
Restrictive lung diseases are characterized by reduced total lung capacity (TLC). TLC represents the amount of air present in the lungs after taking the deepest breath possible. When a restrictive pattern is present, the lungs are "restricted" from fully expanding, making it difficult for a person to take a full breath. Measuring TLC is of critical importance to the diagnosis of restrictive lung disease because it confirms the presence of a true restriction, as well as quantifying the degree of that restriction. Restrictive lung diseases are categorized as intrinsic, extrinsic or neurological.